Many wireless applications require transmission and/or reception on orthogonal linear polarizations. In some applications, transmission is performed with one polarization and reception is performed with an orthogonal polarization in order to provide isolation between the transmitted and received signals. In other application, electromagnetic energy is received on both polarizations and the signals are combined to increase the signal-to-noise ratio, providing polarization diversity gain.
Since a wireless telecommunication system can suffer from multi-path fading, diversity reception is often used to address severe multi-path fading. A diversity technique requires at least two signal paths that carry the same information but have uncorrelated multi-path fadings. Several types of diversity reception are used in base stations, including space diversity, direction diversity, polarization diversity, frequency diversity and time diversity. Polarization diversity uses orthogonal polarization to provide uncorrelated paths. The sense or direction of linear polarization of an antenna is measured from a fixed axis and can vary, depending on system requirements. In particular, the sense of polarization can range from vertical polarization (0 degrees) to horizontal polarization (90 degrees). Conventionally, the most prevalent types of linear polarization used in wireless systems are those which use vertical/horizontal and +45°/−45° polarization (slant 45°). When an antenna assembly receives or transmits signals with two normally orthogonal polarizations, such an antenna assembly is referred to as dual polarized antenna assembly. Such dual polarized antennas must meet a certain port-to-port isolation specification. There is a need for improved port-to-port isolation in dual polarized antennas.